1. Field of the Invention
The present invention relates to a sensor apparatus for detecting contact or proximity of an object (for example, touch sensor), and display devices with the same, and more particularly, to a sensor apparatus and display devices that are intended to achieve higher accuracy of coordinate detection.
2. Description of the Related Art
Display devices including an input apparatus having a function of input through touch operation with a finger or the like (hereinafter, referred to as touch sensor) are used for a portable electronic device, various kinds of home electric appliances, and a stationary customer guiding terminal such as an automatic reception machine. As a detection system for the touch sensor, there are known a resistive film system in which a change in resistance value caused by touch is detected, a capacitive coupling system in which a change in capacitance value is detected, an optical sensor system in which a change in light quantity caused by blocking light is detected, and the like.
In recent years, there have been an increasing number of devices that have a display device including the touch sensor installed therein, and at the same time, there has been increasing a demand for complex functions to be implemented in applications involving the use of the touch sensor. Therefore, a great deal of effort has been taken to expand the number of input points simultaneously detectable by the touch sensor, which has conventionally been a single point, to a plurality of points, in other words, to develop a technology for attaining a multi-touch sensor.
JP 2007-533044 A may be taken as a prior art example that relates to the multi-touch sensor. In the technology disclosed in the prior art example, the capacitive coupling system is employed as the detection system for the touch sensor. The capacitive coupling system is a system in which information obtained by the touch sensor is processed, to thereby individually calculate coordinates of a plurality of input points that are input simultaneously. The touch sensor includes a plurality of X electrodes and a plurality of Y electrodes. The plurality of X electrodes and the plurality of Y electrodes are formed on different layers that are electrically insulated from each other. The plurality of X electrodes each correspond to an X coordinate while the plurality of Y electrodes each correspond to a Y coordinate. Intersections between the plurality of X electrodes and the plurality of Y electrodes serve as detection points in the Cartesian coordinate system. When a conductor such as a finger is brought into contact with the touch sensor, at an intersection between electrodes located in the vicinity of the contact point, a capacitive circuit, in which the X electrode and the Y electrode are coupled to each other via the finger surface, is formed. The capacitive circuit holds a parallel connection to capacitance between the electrodes in a case where there is no contact of the conductor, and as a result, the capacitance between the electrodes increases. In this manner, the increase/decrease in capacitance caused by contact of the detection target object is detected at each intersection between the electrodes, to thereby perform coordinate detection. More specifically, one of the Y electrodes is selected, at which a voltage signal is input, and the signal transmitted so as to be proportional to the capacitance at the intersections between the electrodes is detected at the X electrodes. This step is repeated sequentially for all the Y electrodes, to thereby obtain information on the capacitance at all the intersections in the XY plane. The prior art example describes procedures for calculating coordinates based on the information thus obtained as follows. Four major procedures are provided and are described as follows. (Procedure 1) A detection signal distribution is filtered so as to remove noise. (Procedure 2) Gradient data of the detection signal intensity distribution is generated. (Procedure 3) Boundaries are calculated in the distribution including many input points based on the above-mentioned calculated gradient data. (Procedure 4) Coordinates of each region obtained by separation with the above-mentioned boundaries are calculated.
The processing of Procedure 2 and Procedure 3 in the above-mentioned example is unique to the multi-touch sensor. This is because, as described above, the multi-touch sensor needs to determine a plurality of input points, which are input simultaneously at different positions, as distinct input points. The prior art example discloses that a watershed algorithm is used particularly for Procedure 3, in which the boundaries to be used for determining the input points are calculated. The watershed algorithm is processing of setting markers at minimum points of the gradient of the detection signal intensity distribution obtained in Procedure 2, expanding the markers toward the higher points of the gradient, setting a position at which the markers meet as a boundary line for separating the detection signal distribution, and regarding a region defined thereby as a group.
The above-mentioned prior art example discloses such a signal detection method and processing method for the detection signals as described above, which are used for implementing functions as the multi-touch sensor.